Fluorophores are compounds which generate light as a result of optical excitation. They are used in several fields, such as diagnostic assays. For example, medical diagnostic systems use optical interrogation of fluorophores in assay solutions to measure nucleic acids amplification inside containers such as microfluidic cartridges.
Typically, fluorescent-based processes involve directing excitation light on a specific fluorophore element, which is known to absorb light within a specific excitation wavelength band and emit, as a result, fluorescent light within a different wavelength range. The emitted light is collected and filtered so that only the fluorescence remains and is detected.
For some applications, it is advantageous to use light within different wavelength bands to excite a same assay or sample. This is for example the case when a sample is tested using multiple fluorophores, each having a specific excitation spectral profile. Applications studying other optical phenomena where a sample is excited by light at one wavelength and emits light at another wavelength are also known in the art.
In some cases, it may be desirable for the optical device to be able to switch between different wavelengths rapidly. For example, it is the case with real-time polymerase chain reaction (rtPCR) systems where different samples are mounted circumferentially on a rotating holder for optical analysis. As the holder rotates, fluorescence measurements are performed for each thermal cycle. In order to perform such acquisitions at different wavelengths the interrogation system needs to switch between excitation light sources quickly enough to limit down time between acquisitions, which impacts on the total time of the PCR procedure. Traditional systems using mechanical switching between different light sources or fluorescence filters (such as filter wheels) often introduce substantial delays in the acquisition process. Other systems use different optical interrogation devices altogether for different wavelengths, which can greatly increase the overall cost and complexity of the system.
There is therefore a need for an improved optical excitation and interrogation device allowing the use of different excitation and detection wavelengths and a rapid detection of multiple fluorophores in a sample.